Data Structure Binary Search Tree: Find k-th smallest element in BST (Order Statistics in BST)

http://www.geeksforgeeks.org/find-k-th-smallest-element-in-bst-order-statistics-in-bst/

 1 #include <iostream>

 2 #include <vector>

 3 #include <algorithm>

 4 #include <queue>

 5 #include <stack>

 6 #include <string>

 7 #include <fstream>

 8 #include <map>

 9 using namespace std;

10 

11 struct node {

12     int data;

13     struct node *left, *right;

14     node() : data(0), left(NULL), right(NULL) { }

15     node(int d) : data(d), left(NULL), right(NULL) { }

16 };

17 

18 node *insert(node *root, int key) {

19     if (!root) return new node(key);

20     if (root->data > key) root->left = insert(root->left, key);

21     else root->right = insert(root->right, key);

22     return root;

23 }

24 

25 void prints(node *root) {

26     if (!root) return;

27     prints(root->left);

28     cout << root->data << " ";

29     prints(root->right);

30 }

31 

32 node *k_smallest(node *root, int k) {

33     stack<node*> S;

34     while (1) {

35         while (root) {

36             S.push(root);

37             root = root->left;

38         }

39         if (!S.empty()) {

40             root = S.top();

41             S.pop();

42             if (k-1 == 0) return root;

43             k--;

44             root = root->right;

45         }

46         else break;

47     }

48     return NULL;

49 }

50 

51 int main() {

52     node *root = NULL;

53     root = insert(root, 50);

54     insert(root, 30);

55     insert(root, 20);

56     insert(root, 40);

57     insert(root, 70);

58     insert(root, 60);

59     insert(root, 80);

60     if (k_smallest(root, 5)) cout << k_smallest(root, 5)->data << endl;

61     else cout << "No node" << endl;

62     return 0;

63 }